Which exhaust pollutants are converted by platinum-group metal catalysts?

Platinum-group metals—specifically platinum, palladium, and rhodium—are essential components in automotive catalytic converters. These metals are coated onto honeycomb structures or pellets within the exhaust system to promote the conversion of harmful pollutants into less noxious substances.123

The specific exhaust pollutants converted by these catalysts include:

• Unburned hydrocarbons: These are oxidized into water vapor and carbon dioxide.13
• Carbon monoxide: This is oxidized into carbon dioxide.13
• Nitrogen oxides: These are reduced into nitrogen and oxygen.13

By facilitating these chemical reactions, platinum-group catalysts play a critical role in reducing the discharge of toxic gases from internal-combustion engines.13